Switching power converters including air core coupled inductors

ABSTRACT

A switching power converter includes a first and second switching device, an air core coupled inductor, and a controller. The air core coupled inductor includes a first winding electrically coupled to the first switching device and a second winding electrically coupled to the second switching device. The first and second windings are magnetically coupled. The controller is operable to cause the first and second switching devices to repeatedly switch between their conductive and non-conductive states at a frequency of at least 100 kilohertz to cause current through the first and second windings to repeatedly cycle, thereby providing power to an output port. The switching power converter may have a topology including, but not limited to, a buck converter topology, a boost converter topology, and a buck-boost converter topology.

BACKGROUND

Switching power converters using coupled inductors are known. Forexample, U.S. Pat. No. 6,362,986 to Schultz et al., which isincorporated herein by reference, discloses, among other things,multi-phase DC-to-DC converters including coupled inductors. TheseDC-to-DC converters typically have a higher effective switchingfrequency and lower switching ripple current magnitude thancorresponding DC-to-DC converters using discrete (uncoupled) inductors.

FIG. 1 shows one prior art two-phase buck DC-to-DC converter 100 using acoupled inductor 102. Each phase 104 includes a switching device 106electrically coupled between an input power source 108 and an inductor110. A free wheeling device 112 is electrically coupled between inductor110 and ground, in each phase 104. Each inductor 110 is electricallycoupled to a common output node 114, which includes an output filter116, such as a capacitor.

Each inductor 110 is part of common coupled inductor 102 shared amongphases 104. In particular, each inductor 110 is magnetically coupledwith each other inductor 110 via a magnetic core 118 of coupled inductor102. Each inductor 110 has its own self inductance, often referred to asleakage inductance, which is critical to the operation of DC-to-DCconverter 100. In particular, leakage inductance must be sufficientlylarge to prevent excessive switching ripple current magnitude. On theother hand, if leakage inductance is too large, DC-to-DC converter 100will exhibit poor transient response. As taught in U.S. Pat. No.6,362,986, magnetic coupling between inductors 110 in coupled inductor102 should be sufficiently strong to realize the advantages associatedwith using a coupled inductor, instead of multiple discrete inductors,in DC-to-DC converter 100.

A controller 120 commands switching devices 106 to repeatedly switchbetween their conductive and non-conductive states to regulate thevoltage magnitude on output node 114. Typically, controller 120 isconfigured so that switching devices 106 switch out of phase withrespect to each other to promote cancellation of switching ripplecurrent on output node 114. Free wheeling devices 112 provide a path forcurrent through inductors 110 when switching devices 106 are in theirnon-conductive state.

The frequency at which controller 120 causes switching devices 106 toswitch between their conductive and non-conductive states is referred toas the switching frequency of DC-to-DC converter 100. DC-to-DC converter100 typically operates at a relatively high switching frequency, such asat least 100 kilohertz, to promote low ripple current magnitude, smallsize of coupled inductor 102, small size of output filter 116, and/orfast transient response of DC-to-DC converter 100. In particular, ripplecurrent magnitude decreases as switching frequency increases, so ripplecurrent magnitude can be decreased by increasing switching frequency.Low ripple current magnitude is typically desired because ripple currentcreates losses in components of DC-to-DC converter 100 and ripplevoltage on output node 114.

Additionally, as discussed above, leakage inductance of inductors 110must be sufficiently large so that ripple current magnitude is notexcessively large. However, since ripple current magnitude decreases asswitching frequency is increased, increasing switching frequency mayallow leakage inductance of inductors 110 to be decreased while stillmaintaining an acceptable maximum ripple current magnitude. Decreasingleakage inductance advantageously improves DC-to-DC converter 100'stransient response, and may allow coupled inductor 100 to be madesmaller and/or cheaper. Furthermore, increasing switching frequency mayallow size and/or cost of output filter 116 to be decreased.

Accordingly, there are significant advantages to operating a switchingpower converter using a coupled inductor at a high switching frequency.However, practical limitations typically prevent operating a switchingpower converter at as high of a switching frequency as desired. Forexample, core losses, which are losses in magnetic core 118 of coupledinductor 102 resulting from change in magnetic flux in core 118,typically increase with increasing switching frequency. Core losses areundesirable because they reduce efficiency of DC-to-DC converter 100 andmay cause excessive heating of DC-to-DC converter 100. Thus, core lossesin magnetic core 118 may prevent a switching power converter from beingoperated at as high of a switching frequency as desired.

SUMMARY

In an embodiment, a switching power converter includes a first andsecond switching device, an air core coupled inductor, and a controller.The air core coupled inductor includes a first winding electricallycoupled to the first switching device and a second winding electricallycoupled to the second switching device. The first and second windingsare magnetically coupled. The controller is operable to cause the firstand second switching devices to repeatedly switch between theirconductive and non-conductive states at a frequency of at least 100kilohertz to cause current through the first and second windings torepeatedly cycle, thereby providing power to an output port.

In an embodiment, a switching power converter includes a switchingdevice, a free wheeling device, an air core coupled inductor, and acontroller. The air core coupled inductor includes a first windingelectrically coupled to the switching device and a second windingelectrically coupled to the free wheeling device. The first and secondwindings are magnetically coupled. The controller is operable to causethe first and second switching devices to repeatedly switch betweentheir conductive and non-conductive states at a frequency of at least100 kilohertz to cause current through the first and second windings torepeatedly cycle, thereby providing power to an output port.

In an embodiment, a method for transferring power from an input powerport to an output port in a switching power converter includesrepeatedly switching first and second switching devices out of phasebetween their conductive and non-conductive states at a frequency of atleast 100 kilohertz to cause current flowing through first and secondwindings of an air core coupled inductor to repeatedly cycle, therebytransferring power from the input power port to the output port.

In an embodiment, an air core coupled inductor includes a printedcircuit board and first and second printed circuit board tracesrespectively forming at least partially overlapping first and secondloops in the printed circuit board.

In an embodiment, an air core coupled inductor includes first and secondwires at least partially twisted together and collectively forming aloop. The first and second wires form at least one offset crosssectional area where the first and second wires are not twistedtogether, and the at least one offset cross sectional area is disposedbetween portions of the first and second wires that are twistedtogether.

In an embodiment, an air core coupled inductor includes a printedcircuit board and first and second staple style windings magneticallycoupled and affixed to the printed circuit board.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows one prior art DC-to-DC converter using a coupled inductor.

FIG. 2 is a schematic of one air core coupled inductor, according to anembodiment.

FIG. 3 shows one switching power converter using the air core coupledinductor of FIG. 2, according to an embodiment.

FIG. 4 shows one multi-phase buck converter using the air core coupledinductor of FIG. 2, according to an embodiment.

FIG. 5 shows one multi-phase boost converter using the air core coupledinductor of FIG. 2, according to an embodiment.

FIG. 6 shows one multi-phase buck-boost converter using the air corecoupled inductor of FIG. 2, according to an embodiment.

FIG. 7 shows one Ćuk converter using the air core coupled inductor ofFIG. 2, according to an embodiment.

FIG. 8 shows one air core coupled inductor including two windings,according to an embodiment.

FIG. 9 shows one air core coupled inductor including two wire windingstwisted together, according to an embodiment.

FIG. 10 shows a perspective view of one air core coupled inductorincluding two staple style windings, according to an embodiment.

FIG. 11 shows a perspective view of an alternate embodiment of the aircore coupled inductor of FIG. 10.

FIG. 12 shows an air core coupled inductor similar to the coupledinductor of FIG. 8, but where the windings form two turns, according toan embodiment.

FIG. 13 shows an air core coupled inductor similar to the coupledinductor of FIG. 9, but where the windings form two turns, according toan embodiment.

FIG. 14 shows a perspective view of an air core coupled inductor similarto the coupled inductor of FIG. 11, but where the windings form twoturns, according to an embodiment.

FIG. 15 shows a perspective view of one air core coupled inductorincluding a single staple style conductor, according to an embodiment.

FIG. 16 shows an alternate embodiment of the air core coupled inductorof FIG. 15.

FIG. 17 shows a perspective view of another air core coupled inductorincluding two staple style windings, according to an embodiment.

FIG. 18 shows a plan view of a strip of conductive foil prepared forbending into an embodiment of the coupled inductor of FIG. 17.

FIG. 19 shows a top plan view of a printed circuit assembly including anembodiment of the coupled inductor of FIG. 17.

FIG. 20 shows a perspective view of another air core coupled inductorincluding two staple style windings, according to an embodiment.

FIG. 21 shows a perspective view of yet another air core coupledinductor including two staple style windings, according to anembodiment.

FIG. 22 shows a perspective view of another air core coupled inductorincluding two staple style windings, according to an embodiment.

FIG. 23 shows a perspective view of another air core coupled inductorincluding two staple style windings, according to an embodiment.

FIG. 24 shows a plan view of a strip of conductive foil prepared forbending into an embodiment of the coupled inductor of FIG. 23.

FIG. 25 shows a top plan view of a printed circuit assembly including anembodiment of the coupled inductor of FIG. 23.

FIG. 26 shows a perspective view of another air core coupled inductorincluding two staple style windings, according to an embodiment.

FIG. 27 shows a perspective view of another air core coupled inductorincluding two staple style windings, according to an embodiment

DETAILED DESCRIPTION

As discussed above, switching frequency of a conventional switchingpower converter using a coupled inductor may be limited, at least inpart, due to core losses in the magnetic core of the coupled inductor.However, as discussed below, the present inventor has invented systemsand methods which can, among other things, help overcome thislimitation. In this disclosure, specific instances of an item may bereferred to by use of a numeral in parentheses (e.g., winding 202(1))while numerals without parentheses refer to any such item (e.g.,windings 202).

In particular, the present inventor has determined that switchingfrequency of a switching power converter using a coupled inductor can beincreased by replacing the conventional coupled inductor (e.g., coupledinductor 102 of FIG. 1) with an air core coupled inductor. An air corecoupled inductor differs from a conventional coupled inductor at leastin that windings in an air core coupled inductor are magneticallycoupled together without use of a magnetic core. For example, FIG. 2 isa schematic of an air core coupled inductor 200, including two or morewindings 202, each having a respective first end 204 and a respectivesecond end 206. Each winding 202 has a respective self inductance, orleakage inductance. Additionally, windings 202 are placed sufficientlyclose together so that they are magnetically coupled together withoutuse of a magnetic core. Thus, current entering winding 202(1) from firstend 204(1) induces current in winding 202(2) flowing out of second end206(2), without use of a magnetic core. Similarly, current enteringwinding 202(2) from first end 204(2) induces current flowing in winding202(1) out of second end 206(1), without use of a magnetic core.Accordingly, air core coupled inductor 200 advantageously does notexhibit core losses associated with a conventional coupled inductor,potentially enabling coupled inductor 200 to operate at higher switchingfrequencies than a conventional coupled inductor.

It is anticipated that air core coupled inductor 200 typically will notinclude a magnetic core. However, some embodiments of inductor 200 maynevertheless include one or more cores having minimal effect on magneticcoupling between windings 202, such as one or more cores to increasewinding leakage inductance values. In such embodiments, the windings aresubstantially magnetically coupled together without use of the one ormore magnetic cores, meaning that no more than 10% of a magnetic fieldflux magnetically coupling together the windings flows through the oneor more magnetic cores. Non-magnetic materials other than air (e.g.,cardboard, plastic, printed circuit board material, and/or adhesive) mayseparate windings in air core coupled inductor 200.

Use of an air core coupled inductor, instead of a conventional coupledinductor, in a switching power converter advantageously eliminatescoupled inductor core losses associated with a conventional coupledinductor. Thus, use of an air core coupled inductor, instead of aconventional coupled inductor, may advantageously enable switchingfrequency to be increased, since core losses cannot occur when no coreis present. Increasing switching frequency, in turn, may advantageouslyreduce ripple current magnitude, improve power converter transientresponse, and/or reduce size of filter components. Additionally, an aircore coupled inductor may be simpler and/or cheaper to manufacture thana conventional coupled inductor because the air core coupled inductordoes not include a core which contributes to inductor manufacturingcomplexity and cost. Accordingly, use of an air core coupled inductor,instead of a conventional coupled inductor, in a switching powerconverter may advantageously improve the converter's performance, reducethe converter's size, and/or reduce the converter's cost.

For example, FIG. 3 shows a block diagram of a switching power converter300 using air core coupled inductor 200. Switching power converter 300includes an input power port 302 and an output power port 304. Aswitching device 306 is electrically coupled to at least one winding 202of air core coupled inductor 200, according to the topology of powerconverter 300, as indicated by dashed line 310. At least one winding 202is electrically coupled to output power port 304, according to thetopology of switching power converter 300, as indicated by dashed line312. In the context of this disclosure, a switching device includes, butis not limited to, a bipolar junction transistor, a field effecttransistor (e.g., a N-channel or P-channel metal oxide semiconductorfield effect transistor, a junction field effect transistor, a metalsemiconductor field effect transistor), an insulated gate bipolarjunction transistor, a thyristor, or a silicon controlled rectifier.

A controller 308 causes switching device 306 to periodically switchbetween its conductive and non-conductive states to cause currentthrough first and second windings 202, 204 to repeatedly cycle, therebyproviding power to output power port 304. Controller 308 is optionallyconfigured to also control switching of switching devices 306 toregulate a characteristic of output power port 304, such as voltage ofoutput power port 304 and/or current delivered to a load from outputpower port 304. Examples of topologies of switching power converter 300include a multi-phase buck converter, a multi-phase boost converter, anda multi-phase buck-boost converter, using an air core coupled inductor.Switching power converter 300 could also be a single phase powerconverter of other architecture, such as a Ćuk converter using an aircore coupled inductor. Examples of each of these topologies arediscussed below. However, switching power converter 300 is not limitedto these topologies, and could instead have a different topology usingan air core coupled inductor.

In an exemplary embodiment, FIG. 4 shows one multi-phase buck converter400 using air core coupled inductor 200. Each phase 402 includes aswitching device 404 electrically coupled between an input power port406 and first end 204 of a respective winding 202 of coupled inductor200. Input power port 406 is electrically coupled to an input powersource 407. A free wheeling device 408 is electrically coupled betweenfirst end 204 of winding 202 and a reference node 410 (e.g., ground), ineach phase 402. Each second end 206 of each winding 202 is electricallycoupled to a common output node or port 412. A filter 414, which forexample includes a capacitor, is electrically coupled to output port 412and filters ripple current generated by switching devices 404.

A controller 416 controls operation of buck converter 400. Controller416 controls switching devices 404 via control lines 420. Controller 416causes switching devices 404 to repeatedly switch between theirconductive and non-conductive states to cause current through first andsecond windings 202(1), 202(2) to repeatedly cycle, thereby providingpower to output port 412. Controller 416 also optionally monitors outputport 412 via a feedback line 418 and controls switching of switchingdevices 404 to regulate voltage on output port 412 and/or currentprovided from output port 412 to a load. Controller 416 typicallyoperates buck converter 400 at a switching frequency of at least 100kilohertz to reduce magnitude of ripple current, to minimize size offilter components, and/or to provide fast transient response. Asdiscussed above, the fact that buck converter 400 uses an air corecoupled inductor, instead of a conventional coupled inductor, may enablebuck converter 400 to operate at a higher switching frequency thanconventional multi-phase buck converters using a coupled inductor. Incertain embodiments, controller 416 is operable to control switchingdevices 404 according to a pulse width modulation (PWM) and/or a pulsefrequency modulation (PFM) control scheme. Controller 416 is typicallyconfigured so that switching devices 404 switch out of phase (e.g., 180degrees out of phase) with respect to each other to help cancel ripplecurrent at output port 412.

Free wheeling devices 408 provide a path for current flowing throughwindings 202 after switching devices 404 have turned off. In aparticular embodiment, free wheeling devices 408 are diodes (e.g.,schottky diodes) as shown in FIG. 4. In an alternative embodiment, freewheeling devices 408 are switching devices with appropriate controlcircuitry (e.g., switching devices operating under the command ofcontroller 416). Use of switching devices, instead of diodes, as freewheeling devices 408 may advantageously reduce forward voltage dropacross free wheeling devices 408, since properly selected switchingdevices typically exhibit a lower forward voltage drop than evenschottky diodes. It may also be desirable to use switching devices,instead of diodes, as free wheeling devices 408 to enable continuousconduction mode operation at light load and/or enable buck converter 400to sink current.

FIG. 5 shows a multi-phase boost converter 500 using air core coupledinductor 200. Each phase 502 includes a switching device 504electrically coupled between a second end 206 of a respective winding202 and a reference node 506 (e.g., ground). A first end 204 of eachwinding 202 is electrically coupled to an input power port 508, which isin turn electrically coupled to an input power source 509. Each phase502 further includes a respective free wheeling device 510 electricallycoupled between second end 206 of winding 202 and a common output nodeor port 512. A filter 514, which typically includes a capacitor, is alsoelectrically coupled to output port 512 to filter ripple currentgenerated by switching of switching devices 504.

A controller 516 commands switching devices 504 to repeatedly switchbetween their conductive and non conductive states to cause currentthrough first and second windings 202(1), 202(2) to repeatedly cycle,thereby providing power to output port 512. Controller 516 alsooptionally monitors output port 512 via a feedback line 518 and controlsswitching of switching devices 504 to regulate a characteristic ofoutput port 512 (e.g., voltage at output port 512 and/or currentdelivered to a load from output port 512). Controller 516 interfaceswith switching devices 504 via control lines 520. Controller 516typically operates boost converter 500 at a switching frequency of atleast 100 kilohertz to prevent excessive ripple current magnitude, toallow use of small filter components (e.g., filter 514), and/or topromote fast transient response. In some embodiments, controller 516switches switching devices 504 between their conductive andnon-conductive states according to a PWM and/or a PFM scheme. Controller516 typically switches switching devices 504 out of phase (e.g., 180degrees out of phase) with respect to each other. The fact that boostconverter 500 includes an air core coupled inductor, instead of aconventional coupled inductor, may allow boost converter 500 to operateat a higher switching frequency than conventional boost converters usingcoupled inductors.

Free wheeling devices 510 provide a path for current flowing throughwindings 202 after switching devices 504 have shut off. In a particularembodiment, free wheeling devices 510 are diodes, as shown in FIG. 5. Inan alternative embodiment, free wheeling devices 510 are switchingdevices with appropriate control circuitry (e.g., switching devicesoperating under the command of controller 516), such as to reduceforward voltage drop, enable continuous conduction mode operation atlight load, and/or enable converter 500 to sink current.

FIG. 6 shows a multi-phase buck-boost converter 600 using air corecoupled inductor 200. Each phase 602 includes a switching device 604electrically coupled between an input power port 606 and a first end 204of a respective winding 202 of coupled inductor 200. Input power port606 is electrically coupled to an input power source 607. A second end206 of each winding 202 is electrically coupled to a reference node 608(e.g., ground). Each phase 602 further includes a free wheeling device610 electrically coupled between first end 204 of winding 202 and acommon output node or port 612. A filter 614, which typically includes acapacitor, is also electrically coupled to output port 612 to filterripple current generated by switching of switching devices 604.

A controller 616 commands switching devices 604 to repeatedly switchbetween their conductive and non-conductive states to cause currentthrough first and second windings 202(1), 202(2) to repeatedly cycle,thereby providing power to output power 612. Controller 616 alsooptionally monitors output port 612 via a feedback line 618 and controlsswitching of switching devices 604 to regulate a characteristic ofoutput port 612 (e.g., output voltage on output port 612 and/or currentdelivered to a load from output port 612). Controller 616 interfaceswith switching devices 604 via control lines 620. Controller 616typically operates buck-boost converter 600 at a switching frequency ofat least 100 kilohertz to prevent excessive ripple current magnitude.The fact that buck-boost converter 600 has an air core coupled inductor,instead of a conventional coupled inductor, may advantageously allowbuck-boost converter 600 to operate at higher switching frequencies thanconventional buck-boost converters using coupled inductors. Controller616 typically is configured to switch each switching device 604 out ofphase (e.g., 180 degrees out of phase) with respect to each otherswitching device. In certain embodiments, controller 616 switchesswitching devices 604 according to a PWM and/or a PFM scheme.

Free wheeling devices 610 provide a path for current flowing throughwindings 202 after switching devices 604 turn off. In a particularembodiment, free wheeling devices 610 are diodes, as shown in FIG. 6. Inan alternative embodiment, free wheeling devices 610 are switchingdevices with appropriate control circuitry (e.g., switching devicesoperating under the command of controller 616), such as to reduceforward voltage drop, enable continuous conduction mode operation atlight load, and/or enable converter 600 to sink current.

As discussed above, an air core coupled inductor may also be used in asingle phase switching power converter. FIG. 7 shows a Ćuk converter 700using air core coupled inductor 200. A first end 204(1) of winding202(1) of coupled inductor 200 is electrically coupled to an input powerport 702, and a second end 206(1) of winding 202(1) is electricallycoupled to a switching device 704. Input power port 702 is electricallycoupled to an input power source 703. Switching device 704 iselectrically coupled between second end 206(1) and a reference node 706(e.g., ground). A capacitor 708 is electrically coupled between secondend 206(1) of winding 202(1) and a first end 204(2) of winding 202(2). Asecond end 206(2) of winding 202(2) is electrically coupled to an outputnode or port 710. A filter 712 is also electrically coupled to outputport 710 to filter ripple current generated by switching of switchingdevice 704. A free wheeling device 714 is electrically coupled betweenfirst end 204(2) of winding 202(2) and reference node 706. Free wheelingdevice 714 provides a path for current flowing through winding 202(2)when switching device 704 turns off.

A controller 716 causes switching device 704 to repeatedly switchbetween its conductive and non-conductive states to cause currentthrough first and second windings 202(1), 202(2) to repeatedly cycle,thereby providing power to output port 710. Controller 716 alsooptionally monitors output port 710 via a feedback line 718 and controlsswitching of switching device 704 to regulate a characteristic of outputport 710 (e.g., voltage on output port 710 and/or current flowing fromoutput port 710 to a load), typically at a switching frequency of atleast 100 kilohertz to prevent excessive ripple current magnitude.Controller 716 interfaces with switching device 704 via a control line720. In certain embodiments, controller 716 switches switching device704 between its conductive and non-conductive states according to a PWMand/or a PFM scheme. In a particular embodiment, free wheeling device714 is a diode, as shown in FIG. 7. In an alternative embodiment, freewheeling device 714 is a switching device with appropriate controlcircuitry (e.g., a switching device operating under the command ofcontroller 716), such as to reduce forward voltage drop across freewheeling device 714.

Discussed below are a number of examples of how the air core coupledinductors disclosed herein can be configured. For example, air corecoupled inductor 200 could take the form of air core coupled inductor800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 2000, 2100,2200, 2300, 2600, or 2700, discussed below. However, it should beappreciated that the air core coupled inductors of this disclosure canbe configured in other manners and are therefore not limited to theseexamples.

FIG. 8 shows one air core coupled inductor 800 including two windings802, 804 forming respective loops. Winding 804 is shown as a dashed linein FIG. 8 to distinguish it from winding 802. Windings 802, 804 are, forexample, formed conductive wire, foil, or bars. In some embodiments,windings 802, 804 are conductive circuit traces of a printed circuitboard (PCB).

The loops of windings 802, 804 typically do not completely overlap, asshown in FIG. 8, to increase leakage inductance values of windings 802,804, since leakage inductance must be sufficiently large to preventexcessive ripple current magnitude. In particular, coupled inductor 800typically includes one or more offset cross sectional areas 806, wheremagnetic field flux generated by one of windings 802, 804 is notsubstantially magnetically coupled to the other of windings 802, 804.Thus, leakage inductance can be varied by varying the configuration ofoffset cross sectional areas 806. For example, leakage inductance can beincreased by increasing the size of offset cross sectional areas 806.

It is anticipated that in many embodiments, offset cross sectional areas806(1), 806(2) will have a similar size and shape so that the respectiveleakage inductance values associated with windings 802, 804 areapproximately equal. However, asymmetrical leakage inductance values maybe desired in certain applications, and offset cross sectional areas806(1), 806(2) may have different sizes and/or shapes so that therespective leakage inductance values associated with windings 802, 804are different. For example, if offset cross sectional area 806(2) ismade significantly larger than offset cross sectional area 806(1),leakage inductance associated with winding 804 will be larger than thatassociated with winding 802, since offset cross sectional area 806(2)primarily contributes to leakage inductance associated with winding 804,and offset cross sectional area 806(1) primarily contributes to leakageinductance associated with winding 802.

Air core coupled inductor 800 also includes common cross sectional area808, where magnetic field flux generated by one of windings 802, 804 issubstantially magnetically coupled to the other of windings 802, 804.Accordingly, magnetizing inductance can be varied by varying theconfiguration of common cross sectional area 808. For example,magnetizing inductance can be increased by increasing the size of commoncross sectional area 808.

It is anticipated that alternate embodiments of air core coupledinductor 800 will have different winding shapes (e.g., circular, oval,trapezoidal, etc.). The number of common and/or offset cross sectionalareas 806, 808 could also be varied. For example, an additional offsetcross sectional area could be added to increase leakage inductance ofwindings 802, 804.

FIG. 9 shows an air core coupled inductor 900 including two conductivewire windings 902, 904 at least partially twisted or wound together toestablish magnetic coupling between wires 902, 904. Wire 902 is shown inFIG. 9 as being thinner than wire 904 to distinguish wires 902, 904 inthe figure. However, it is anticipated that most embodiments of coupledinductor 900 will have wires 902, 904 of the same thickness (i.e., ofthe same wire gauge). Wires 902, 904 collectively form a loop, as shownin FIG. 9.

Air core coupled inductor 900 may be particularly useful in applicationswhere components are physically separated from each other, but need tobe electrically coupled together. In such applications, air coupledinductor 900 could serve dual roles as (1) an electrical connectorelectrically coupling together the physically separated components, and(2) a coupled inductor, thereby promoting low cost and space savings byachieving two functions with a single component.

Wires 902, 904 are typically not completely twisted together to increaseleakage inductance values associated with windings 902, 904. Forexample, FIG. 9 shows wires 902, 904 including two offset crosssectional areas 906, 908 where wires 902, 904 are not twisted togetherand are spaced apart. Offset cross sectional areas 906, 908 are disposedbetween portions of wires 902, 904 that are twisted together. Offsetcross sectional area 906 primarily boosts leakage inductance associatedwith wire 902, and offset cross sectional area 908 primarily boostsleakage inductance associated with wire 904. Similar to coupled inductor800 (FIG. 8), offset cross sectional areas 906, 908 may have a similarsize and shape so that the respective leakage inductance valuesassociated with wires 902, 904 are approximately equal. Alternately,offset cross sectional areas 906, 908 may have different sizes and/orshapes so that the respective leakage inductance values associated withwires 902, 904 are different.

It should be appreciated that the number and/or configuration of offsetcross sectional areas may be varied to adjust leakage inductance valuesassociated with wires 902, 904. For example, leakage inductance can beincreased by adding additional offset cross sectional areas.

Air core coupled inductor 900 also includes a common cross sectionalarea 910, where magnetic field flux generated by one of wires 902, 904is substantially magnetically coupled to the other of wires 902, 904.Accordingly, magnetizing inductance can be varied by varying theconfiguration of common cross sectional area 910. For example,magnetizing inductance can be increased by increasing the size of commoncross sectional area 910.

FIG. 10 shows an air core coupled inductor 1000 including two staplestyle windings 1002, 1004, which are optionally affixed to a PCB 1005.As shown in FIG. 10, windings 1002, 1004 are aligned along lengthwiseaxis 1006 of windings 1002, 1004. However the relative position ofwindings 1002, 1004 can be varied to vary leakage and magnetizinginductance values. For example, FIG. 11 shows an air core coupledinductor 1100, which is the similar to coupled inductor 1000 (FIG. 10),but with windings 1002, 1004 offset along axis 1006. Therefore, coupledinductor 1100 will have larger leakage inductance values and a smallermagnetizing inductance value than inductor 1000, since a smaller portionof windings 1002, 1004 are aligned along axis 1006 in inductor 1100 thanin inductor 1000. It should also be noted that magnetizing inductancecould be increased without significantly affecting leakage inductance byincreasing the length of both windings 1002, 1004 along axis 1006. Eachwinding 1002, 1004 optionally forms a solder tab 1008, 1010, 1012, and1014 at its ends, as shown in FIG. 10. Solder tabs 1008, 1010, 1012, and1014 are each configured for surface mount attachment to a PCB.

It is anticipated that certain embodiments of the coupled inductorsdisclosed herein will have windings with more than one turn. Increasingthe number of turns can be used to increase inductance values and/ordecrease inductor size while maintaining acceptably high inductancevalues. For example, FIG. 12 shows a coupled inductor 1200, which issimilar to coupled inductor 800 (FIG. 8), but with windings 1202, 1204each forming two turns or loops. FIG. 13 shows a coupled inductor 1300,which is similar to coupled inductor 900 (FIG. 9), but with windings1302, 1304 collectively forming two turns or loops. FIG. 14, in turn,shows a coupled inductor 1400, which is similar to coupled inductor 1100(FIG. 11), but with windings 1402, 1404 each forming two turns.

Certain embodiments of the air core coupled inductors disclosed hereintake the form of a single structure. For example, FIG. 15 shows an aircore coupled inductor 1500 including a single staple style conductor1502. Conductor 1500 can be configured as two separate windingsmagnetically coupled together without use of a magnetic core. Forexample, if coupled inductor 1500 were used in a multi-phase buckconverter (e.g., buck converter 400 of FIG. 4), portion 1504 ofconductor 1502 would typically be connected to a first switching node(e.g., switching node 422(1) of FIG. 4), portion 1506 would typically beconnected to a second switching node (e.g., switching node 422(2) ofFIG. 4), and common section or portion 1508 would typically be connectedto a common output node (e.g., output port 412 of FIG. 4). Portions1504, 1506, and 1508 optionally form solder tabs configured for surfacemount soldering to a PCB, as shown in FIG. 15.

The alignment and/or length of sections of conductor 1502 can be variedto vary leakage and/or magnetizing inductance. For example, FIG. 16shows an air core coupled inductor 1600, which is similar to coupledinductor 1500, but includes a single conductor 1602 that can beconfigured as an air core coupled inductor with windings having twoturns. Section 1604 of conductor 1602 is offset relative to section 1606of conductor 1602 along lengthwise axis 1608 of the windings to increaseleakage inductance and to decrease magnetizing inductance. If coupledinductor 1600 were used in a multi-phase buck converter, portion 1610 ofconductor 1602 would typically be connected to a first switching node(e.g., switching node 422(1) of FIG. 4), portion 1612 would typically beconnected to a second switching node (e.g., switching node 422(2) ofFIG. 4), and a common section or portion 1614 would typically beconnected to a common output node (e.g., output port 412 of FIG. 4).Portions 1610, 1612, and 1614 optionally form solder tabs configured forsurface mount soldering to a PCB, as shown in FIG. 16.

FIG. 17 shows another air core coupled inductor 1700 including twostaple style windings 1702, 1704 connected via a conductive commonsection 1706. In certain embodiments, air core coupled inductor 1700 isa single structure (e.g., windings 1702, 1704 and common section 1706are part of a single piece of conductive foil), thereby promoting easeof manufacturing and installation of coupled inductor 1700. For example,FIG. 18 shows a plan view of a strip 1800 of conductive foil preparedfor bending into an embodiment of coupled inductor 1700. Solid line 1802indicates where strip 1800 has been cut, and the dashed lines (notlabeled) indicate where strip 1800 is to be bent. Strip 1800'srectangular shape promotes efficient resource utilization duringmanufacturing since commercially available conductive foil typically hasa rectangular shape.

Returning to FIG. 17, a distal end of each winding 1702, 1704 forms asolder tab 1708, 1710 configured for surface mount attachment to a PCB.Conductive common section 1706 is configured for surface mountattachment to a PCB, and common section 1706 can therefore supplement orreplace one or more PCB circuit traces. It is anticipated that aconductive foil forming coupled inductor 1700 will typically besignificantly thicker than a PCB circuit trace. Thus, common section1706 will typically have a significantly lower resistance than asimilarly sized/shaped PCB circuit trace, since common section 1706 istypically significantly thicker than a PCB circuit trace. Therefore, useof common portion 1706 as a supplement to or a substitute for one ormore PCB circuit trace may significantly lower system resistance. Ifcoupled inductor 1700 were used in a multi-phase buck converter, soldertab 1708 would typically be connected to a first switching node (e.g.,switching node 422(1) of FIG. 4), solder tab 1710 would typically beconnected to a second switching node (e.g., switching node 422(2) ofFIG. 4), and common section 1706 would typically be connected to acommon output node (e.g., output port 412 of FIG. 4).

In certain embodiments, a separation distance 1712 between solder tabs1708, 1710 is relatively small, thereby potentially enabling switchingstages to be located close together, since switching stages should belocated near their respective winding ends to minimize interconnectionlosses and ringing. Placing switching stages close together may bedesirable in certain applications, such as where multiple switchingstages share a common heatsink. FIG. 19 shows a top plan view of aprinted circuit assembly 1900, which is one possible two-phase buckconverter application of coupled inductor 1700. Assembly 1900 includes aPCB 1902, switching stages 1904, 1906, and an embodiment of coupledinductor 1700. The relatively small separation distance 1712 betweensolder tabs 1708, 1710 enables switching stages 1904, 1906 to be locatedclose together while still being located close to ends of theirrespective windings 1702, 1704.

The alignment and/or length of windings 1702, 1704 can be varied duringthe design of coupled inductor 1700 to vary leakage inductance and/ormagnetizing inductance. For example, magnetizing inductance may beincreased by increasing portions of windings 1702, 1704 that are alignedwith each other along lengthwise axis 1714 of windings 1702, 1704. Asanother example, leakage inductance associated with windings 1702, 1704can be increased by increasing portions of windings 1702, 1704 that areoffset from each other along axis 1714.

FIG. 20 shows an air core coupled inductor 2000 including two staplestyle windings 2002, 2004 connected via a conductive common section2006. Coupled inductor 2000 is similar to coupled inductor 1700 (FIG.17) but differs in that windings 2002, 2004 of coupled inductor 2000connect to the outside of common section 2006, while windings 1702, 1704of coupled inductor 1700 connect to the inside of common section 1706.Therefore, for a given winding length and common section size, coupledinductor 2000 may have a smaller footprint than coupled inductor 1700. Adistal end of each winding 2002, 2004 forms a solder tab 2008, 2010configured for surface mount attachment to a PCB. In certain embodimentsof coupled inductor 2000, windings 2002, 2004 and common section 2006are part of a single piece of conductive foil.

FIG. 21 shows an air core coupled inductor 2100, which is similar tocoupled inductor 2000 (FIG. 20), but with extended solder tabs 2102,2104. Specifically, solder tabs 2102, 2104 extend along a widthwise axis2106 in coupled inductor 2100. Such extended solder tabs may replaceand/or supplement PCB circuit traces in applications where coupledinductor 2100 is installed on a PCB. Similar to coupled inductor 2000(FIG. 20), coupled inductor 2100 includes two staple style windings2108, 2110 connected via a conductive common section 2112. It isanticipated that in many embodiments of coupled inductor 2100, windings2108, 2110 and common section 2112 will be part of a single piece ofconductive foil.

FIG. 22 shows an air core coupled inductor 2200, which is similar tocoupled inductor 2100 (FIG. 21), but where only one solder tab 2202extends along a widthwise axis 2204 of coupled inductor 2200. Solder tab2206, in contrast, has a configuration similar to that of solder tab2010 (FIG. 20). Similar to coupled inductor 2000 (FIG. 20), coupledinductor 2200 includes a two staple style windings 2208, 2210 connectedvia a conductive common section 2212, and it is anticipated that each ofsuch components will typically be part of a single piece of conductivefoil.

FIG. 23 shows another air core couple inductor 2300 including two staplestyle windings 2302, 2304 connected via a conductive common section2306. It is anticipated that many embodiments of coupled inductor 2300will be formed from a single piece of conductive foil. For example, FIG.24 shows a plan view of a strip 2400 of conductive foil prepared forbending into an embodiment of coupled inductor 2300. The dashed lines(not labeled) indicate where strip 2400 is to be bent. Although strip2400 is not rectangular, its shape still promotes efficient utilizationof conductive foil, thereby promoting efficient resource utilizationduring manufacturing.

Returning to FIG. 23, a distal end of each winding 2302, 2404 forms asolder tab 2308, 2310 configured for surface mount attachment to a PCB.Conductive common section 2306 is configured for surface mountattachment to a PCB, and common section 2306 can therefore supplement orreplace one or more PCB traces. If coupled inductor 2300 were used in amulti-phase buck converter, solder tab 2308 would typically be connectedto a first switching node (e.g., switching node 422(1) of FIG. 4),solder tab 2310 would typically be connected to a second switching node(e.g., switching node 422(2) of FIG. 4), and common section 2306 wouldtypically be connected to a common output node (e.g., output port 412 ofFIG. 4).

It is anticipated that a separation distance 2314 between solder tabs2308, 2310 will typically be relatively large. Accordingly, certainembodiments of coupled inductor 2300 may be well suited for applicationswhere it is desired that switching stages be widely separated. FIG. 25shows a top plan view of a printed circuit assembly 2500, which is onepossible two-phase buck converter application of coupled inductor 2300.Assembly 2500 includes a PCB 2502, switching stages 2504, 2506, and anembodiment of coupled inductor 2300. The relatively large spacing 2314between solder tabs 2308, 2310 enables switching stages 2504, 2506 to belocated relatively far apart, while still being located close to ends oftheir respective windings 2302, 2304.

The alignment and/or length of windings 2302, 2304 can be varied duringthe design of coupled inductor 2300 to vary leakage inductance and/ormagnetizing inductance. For example, magnetizing inductance may beincreased by increasing portions of windings 2302, 2304 that are alignedwith each other along lengthwise axis 2312 of windings 2302, 2304. Asanother example, leakage inductance associated with windings 2302, 2304can be increased by increasing portions of windings 2302, 2304 that areoffset from each other along axis 2312.

FIG. 26 shows an air core coupled inductor 2600. Coupled inductor 2600is similar to coupled inductor 2300 (FIG. 23) but includes extendedsolder tabs 2602, 2604. Coupled inductor 2600 includes staple stylewindings 2606, 2608 connected via a conductive common section 2610. Adistal end of each winding 2606, 2608 forms a respective solder tab2602, 2604 configured for surface mount attachment to a PCB. Solder tabs2602, 2604 extend along a widthwise axis 2612 of coupled inductor 2600.Extended solder tabs 2602, 2604 may supplement or replace a PCB circuittrace in applications where coupled inductor 2600 is installed on a PCB.Windings 2606, 2608 and common section 2610 are, for example, part of asingle piece of conductive foil, thereby promoting low cost andmanufacturability of coupled inductor 2600.

FIG. 27 shows another air core coupled inductor 2700, which is similarto coupled inductor 2600 (FIG. 26), but where only one solder tab 2702extends along a widthwise axis 2704 of coupled inductor 2700. Solder tab2706, in contrast, has a configuration similar to that of solder tab2310 (FIG. 23). Similar to coupled inductor 2600 (FIG. 26), coupledinductor 2700 includes a two staple style windings 2708, 2710 connectedvia a conductive common section 2712, and it is anticipated thatwindings 2708, 2710 and common section 2712 will typically be part of asingle piece of conductive foil.

Changes may be made in the above methods and systems without departingfrom the scope hereof. For example, particular alternative embodimentsof coupled inductors 1100, 1400, 1500, and 1600 could haveconfigurations that are mirror images of those shown in FIGS. 11, 14,15, and 16, respectively. As another example, windings 1702, 1704 couldtrade positions along widthwise axis 1716 in an alternative embodimentof coupled inductor 1700 (FIG. 17). Similar modifications are possiblein alternative embodiments of coupled inductors 2000, 2100, 2200, 2300,2600, and 2700. Therefore, the matter contained in the above descriptionand shown in the accompanying drawings should be interpreted asillustrative and not in a limiting sense. The following claims areintended to cover generic and specific features described herein, aswell as all statements of the scope of the present method and system,which, as a matter of language, might be said to fall therebetween.

What is claimed is:
 1. A switching power converter, comprising: a firstand second switching device; an air core coupled inductor including: afirst winding electrically coupled to the first switching device, and asecond winding electrically coupled to the second switching device, thefirst and second windings magnetically coupled; and a controlleroperable to cause the first and second switching devices to repeatedlyswitch between their conductive and non-conductive states at a frequencyof at least 100 kilohertz to cause current through the first and secondwindings to repeatedly cycle, thereby providing power to an output port.2. The switching power converter of claim 1, the first and secondwindings being magnetically coupled without use of a magnetic core. 3.The switching power converter of claim 1, the controller operable tocause the first and second switching devices to switch out of phase withrespect to each other.
 4. The switching power converter of claim 1,further comprising: a first free wheeling device electrically coupledbetween a first end of the first winding and a reference node; and asecond free wheeling device electrically coupled between a first end ofthe second winding and the reference node, the first switching devicebeing electrically coupled between an input power port and the first endof the first winding, the second switching device being electricallycoupled between the input power port and the first end of the secondwinding, and a second end of the first winding and a second end of thesecond winding being electrically coupled to the output port.
 5. Theswitching power converter of claim 4, the first and second windingsrespectively comprising first and second printed circuit board traces,the first and second printed circuit board traces respectively formingat least partially overlapping first and second loops in the printedcircuit board.
 6. The switching power converter of claim 5, the firstand second loops only partially overlapping.
 7. The switching powerconverter of claim 4, the first and second windings respectivelycomprising first and second wires at least partially twisted together.8. The switching power converter of claim 7, the first and second wiresforming at least one offset cross sectional area where the first andsecond wires are not twisted together and are spaced apart, the at leastone offset cross sectional area being disposed between portions of thefirst and second wires that are twisted together.
 9. The switching powerconverter of claim 4, further comprising a printed circuit board, andthe first and second windings respectively comprising first and secondstaple style windings affixed to the printed circuit board.
 10. Theswitching power converter of claim 9, the first and second staple stylewindings being part of a single piece of conductive foil including acommon section electrically coupled to the output port.
 11. Theswitching power converter of claim 1, further comprising: a first freewheeling device electrically coupled between a second end of the firstwinding and the output port; and a second free wheeling deviceelectrically coupled between a second end of the second winding and theoutput port, the first switching device being electrically coupledbetween the second end of the first winding and a reference node, thesecond switching device being electrically coupled between the secondend of the second winding and the reference node, a first end of thefirst winding and a first end of the second winding being electricallycoupled to an input power port.
 12. The switching power converter ofclaim 11, the first and second windings respectively comprising firstand second printed circuit board traces, the first and second printedcircuit board traces respectively forming at least partially overlappingfirst and second loops in the printed circuit board.
 13. The switchingpower converter of claim 12, the first and second loops only partiallyoverlapping.
 14. The switching power converter of claim 11, the firstand second windings respectively comprising first and second wires atleast partially twisted together.
 15. The switching power converter ofclaim 14, the first and second wires forming at least one offset crosssectional area where the first and second wires are not twisted togetherand are spaced apart, the at least one offset cross sectional area beingdisposed between portions of the first and second wires that are twistedtogether.
 16. The switching power converter of claim 11, furthercomprising a printed circuit board, and the first and second windingsrespectively comprising first and second staple style windings affixedto the printed circuit board.
 17. The switching power converter of claim16, the first and second staple style windings being part of a singlepiece of conductive foil including a common section electrically coupledto the input power port.
 18. The switching power converter of claim 1,further comprising: a first free wheeling device electrically coupledbetween a first end of the first winding and the output port; and asecond free wheeling device electrically coupled between a first end ofthe second winding and the output port, the first switching device beingelectrically coupled between an input power port and the first end ofthe first winding, the second switching device being electricallycoupled between the input power port and the first end of the secondwinding, and a second end of the first winding and a second end of thesecond winding being electrically coupled to a reference node.
 19. Theswitching power converter of claim 18, the first and second windingsrespectively comprising first and second printed circuit board traces,the first and second printed circuit board traces respectively formingat least partially overlapping first and second loops in the printedcircuit board.
 20. The switching power converter of claim 19, the firstand second loops only partially overlapping.
 21. The switching powerconverter of claim 18, the first and second windings respectivelycomprising first and second wires at least partially twisted together.22. The switching power converter of claim 21, the first and secondwires forming at least one offset cross sectional area where the firstand second wires are not twisted together and are spaced apart, the atleast one offset cross sectional area being disposed between portions ofthe first and second wires that are twisted together.
 23. The switchingpower converter of claim 18, further comprising a printed circuit board,and the first and second windings respectively comprising first andsecond staple style windings affixed to the printed circuit board. 24.The switching power converter of claim 23, the first and second staplestyle windings being part of a single piece of conductive foil includinga common section electrically coupled to the reference node.